The present invention relates to a system and method of mapping irregularities of hard tissue. Specifically, the invention relates to detecting irregularities in hard tissue such as bone (e.g. fractures, joint abnormalities and implanted surgical anchors.)
According to the American Academy of Orthopaedic Surgeons, every year approximately 6.5 million bone fracture cases are diagnosed in the United States alone. Orthopedic medicine has traditionally relied upon radiographic images (e.g. X-Ray or CT scan) of bone tissue as a means of diagnosing bone abnormalities including fractures and malformations. These methods require exposing a patient to radiation.
U.S. Pat. No. 4,798,210 issued to Ledley describes a method for developing a 3D image of a 3D object using ultrasound whereby a first image is combined with a second image in order to create a 3D image. Again, teachings of Ledley contain neither a hint nor suggestion that renderings of bone or imperfections therein may be produced by ultrasound.
U.S. Pat. No. 5,924,989 issued to Polz is an additional example of a three dimensional ultrasonic system for capturing images of dynamic organs such as the heart or other parts of the respiratory system. Like Ledley, Polz employs a combination of different images in order to complete the three dimensional image. Again, teachings of Polz contain neither a hint nor suggestion that renderings of bone or imperfections therein may be produced by ultrasound.
U.S. Pat. No. 5,928,151 issued to Hossack et al. is a further example of a three dimensional ultrasonic scanning system. Again, teachings of this patent contain neither a hint nor suggestion that renderings of bone or imperfections therein may be produced by ultrasound. The opposite is true, the emphasis on the ability to work without contrast agents suggests that Hossack envisioned only soft tissue applications.
U.S. Pat. No. 6,120,453 issued to Sharp is a three-dimensional ultrasound system. The teachings of this patent are similar to those of Ledley and Polz. Again, Sharp employs the combination of several images to create a three dimensional image. Again, Sharp offers neither a hint nor suggestion that renderings of bone or imperfections therein may be produced by ultrasound.
In summary, none of the patents in this first group even imply that generation maps of irregularities of bone can be generated using ultrasound technology. Instead, they stress various means of increasing resolution of 3D images of soft tissue. Application of these methods directly to hard tissue is impractical because the echo reflection properties of soft tissue are not similar to those of hard tissue.
The concept of ultrasonic imaging of bone is also not unknown. However, bone images produced by ultrasound are typically not three dimensional as exemplified by this second group of prior art references.
U.S. Pat. No. 4,476,873 issued to Sorenson et al. is an ultrasound scanning system used for imaging skeletal structure. This scanning system can distinguish between hard and soft tissue and is used to detect scoliosis. However, FIGS. 14–18 of this patent make it abundantly clear that while data may be collected in three dimensions, output is supplied as graphs. Thus, it is an inherent disadvantage of Sorenson that images are not provided as a result of the scan. Sorenson teaches differentiation between lungs containing air and bones. It will be appreciated that lung tissue, which presents alternating layers of air and soft tissue, is more different from bone than other soft tissues such as muscle. Further, Sorenson teaches that Snell's law typically causes most transmitted energy to be reflected along a line which is at an angle to a longitudinal axis of the transmitting transducer. Therefore, Sorenson teaches extensive amplification of the small amount of reflected energy returning along this axis or, in the alternative, capture of reflected energy at one or more additional transducers. Thus, Sorenson teaches determination of co-ordinates of a point in three degrees of freedom, as opposed to six degrees of freedom. Thus changes in an angle of a surface over distance are not determined by these teachings. This is a distinct and inherent disadvantage which renders these teachings unsuitable to use in imaging surface irregularities of long bones.
U.S. Pat. No. 5,140,988 issued to Stouffer et al. is a method and apparatus for imaging bone structures in animal carcasses. FIGS. 2 and 3 of this patent demonstrate that the teachings of Stouffer relate to 2 dimensional images of bone. Stouffer fails to teach imaging of irregularities in bone surface such as fractures.
U.S. Pat. No. 5,840,029 issued to Mazess et al is a method for using ultrasound to measure bone. Mazess concerns himself primarily with measurement of bone properties. Mazess fails to teach imaging of irregularities in bone surface such as fractures.
U.S. Pat. No. 5,879,301 issued to Chibrera et al. is a method for detecting the properties of bone using ultrasound, specifically for detecting osteoporosis. It is an inherent disadvantage of Chibrera that production of images of measured bones, or surface irregularities thereof is not taught.
U.S. Pat. No. 6,015,383 issued to Buhler et al. teaches acoustic analysis to detect the characteristics of bone tissue where the edge of the bone is detected. However, FIGS. 3–6 of this patent make it abundantly clear that output is supplied as graphs. Thus, it is an inherent disadvantage of Buhler that images are not provided as a result of the scan.
U.S. Pat. No. 322,507 issued to Passi et al. is an ultrasonic system for evaluation of bone tissue. Like other patents in this group, it has the inherent disadvantage of providing output as graphs rather than images. Further, measurements according to these teachings are of acoustic properties and not of surface position co-ordinates.
Thus, while members of this second group of patents teach assays of bone using ultrasound technology, they fail to teach production of maps of surface irregularities in bone.
Additional patents dealing with ultrasonic imaging of bone are presented hereinbelow.
U.S. Pat. No. 5,305,752 issued to Spivey is a system for imaging tissue in the body using acoustic waves. While Spivey teaches formation of a single ultrasonic image depicting both soft tissue and bone, the image is a cross-sectional image (i.e. 2 dimensional). Spivey does not teach imaging of surface irregularities such as fractures.
U.S. Pat. No. 5,465,722 issued to Fort et al. relates to a 3D ultrasonic system. Although these teachings included production of a 3D image of a bone (FIG. 13), they do not include imaging of surface irregularities such as fractures. U.S. Pat. No. 6,375,616 issued to Soferman et al. is a method for determining fetal weight in utero. Although Soferman teaches application of grey level threshold in order to isolate bones from other tissue in an image, his teachings do not include imaging of surface irregularities such as fractures.
U.S. Pat. No. 6,390,982 issued to Bova et al. is a method of creating a three dimensional image. The teachings of Bova are directed to ultrasonic probes as an adjunct to a second imaging technology in localizing bone. This means that generation of the three dimensional image from ultrasound image data alone is beyond the scope of Bova's teachings. Further, Bova does not teach imaging of surface irregularities such as fractures.
U.S. Pat. No. 6,413,215 issued to Wu et al. is an ultrasonic system for detecting the wear of artificial joints. The teachings of Wu rely upon scattering of ultrasonic energy as a result of cavitation events in synovial fluid. Further, Wu teaches output of data as particle size information, not particle position. In summary, these teachings have little relevance to the instant application because cavitation events are not expected to occur in typical measurement of hard tissue surface irregularities.
There is thus a widely recognized need for, and it would be highly advantageous to have, a system and method mapping irregularities of hard tissue devoid of the above limitations.